1. Field of the Invention
The invention relates to the field of computer system communications, and in particular, to a concentrator and protocol converter for concentrating signals from a number of sources in a computer system into one serial interface, and for converting communication protocols to enable communication between devices with differing protocol specifications.
2. Background Information
Many computer systems are designed and built to have a number of different possible configurations, for example the IBM AS/400 system (IBM and AS/400 are registered trademarks of International Business Machines Corporation). The configurations may vary in number of processors, amount of memory, number of I/O devices, and in the required amounts of power, cooling and/or power sequencing. It may be necessary to detect that certain components are present and correctly configured for the particular processor type used in the system. In the past, such configuration information was determined from configuration pins on backplanes or processor cards, for example. However this method is limited by the number of available pins and the effort required to change the configuration ID. It may require that expensive components be changed to force a change in the configuration ID when there was no other reason to change the component.
The various processing elements of the computer system, including racks and/or towers, may be interconnected by a control network, e.g., the system power control network (SPCN). The SPCN was designed as a low volume serial network used to monitor power conditions at a plurality of nodes in a computer system of racks/towers, in particular, the IBM AS/400. The nodes typically include microprocessors which monitor the status of, and make occasional adjustments to, the power conditions at the respective nodes. A tower is a small rack typically containing a tower node processor and only one slave processor, while a rack typically contains a rack node processor and several slave processors. A primary rack or tower of the network also contains a central electronics complex (CEC) with the network "master" processor, as well as the computer system CPU. Such a network is the subject matter of the inventor's prior U.S. Pat. No. 5,117,430, and an improved network is the subject matter of the inventor's co-pending related application, referenced above.
The solution to the above problems associated with using configuration pins, which is the subject matter of the related co-pending application referenced above, is to add information circuits, in particular, VPD (Vital Product Data) chips, to the computer system (e.g., an IBM AS/400) processors, backplanes, and memory cards, to store various configuration and asset information (vital product data), such as power and cooling requirements, and provide this information to the computer system. It may also be desirable, for example, to add these VPD chips to other cards in the Central Electronics Complex (CEC--the site of the host CPU), and to expansion towers of the computer system.
One particular type of VPD chip is referred to herein as the "smart card" VPD chip. This chip provides secure, i.e., encrypted, data storage, and communicates with outside devices using a half-duplex asynchronous block protocol, such as described in ISO 7816-3. However, this communications standard provides limited addressability, and for electrical loading and performance reasons, a large number of VPD chips cannot be connected to a common, i.e., multi-dropped, interface. Further, since failures on a multi-dropped interface could preclude communication with all chips, and since communication with a subset of the VPD chips is required to successfully operate the computer system, a more robust design uses point-to-point interfaces. However, using point-to-point interfaces in turn creates the need to concentrate a large number of point-to-point interfaces to a common point for communication with the computer system.
The smart card VPD chip protocol uses unique error detection and recovery at the protocol layer that is best hidden from the application layers of the computer system, which are only interested in the data which is stored in the chips.
Therefore, a need existed for a way of concentrating the signals from the Smart card VPD chips to a computer system control point, and further a way of handling the special protocol requirements of the smart card VPD chips within the existing computer system's network protocol, e.g., SPCN (System Power Control Network) protocol.